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Патент USA US2129841

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Patented Sept. 13, 1938
2,129,841 .
Carl E. Hillers, Charlottesville, Va., assignor to
Blue Ridge Slate Corporation, Charlottesville,
Va., a corporation'of Virginia
No Drawing.
Application March 21, 1935, '
Serial No. 12,255
8 Claims.
This invention relates to new and useful immovements in colored silicate vcoatings on re
fractory granular material.
The object of the present invention is to pre
5 vent or to diminish the tendency of such coatings
to bloom. Blooming is a characteristic defect of
many types of coatings produced from sodium
silicate, and I accomplish my object by incor
porating boric acid or boric oxide with the sodium
10" silicate in the coating of the granules, thus pro
ducing under proper heating conditions a marked
reduction in ‘carbonate blooming tendency. Fur
(0]. 91-70)
sodium silicate that it loses its adhesive quality.
If a saturated solution of boric acid is added,
precipitation ‘occurs and, due to dilution, the so
' dium silicate loses much of its adhesive quality.
As the addition is continued, and sometimes 5
merely upon standing, gell formation takes place.
Granules coated with such gells will not make a
satisfactory commercial product unless they are
processed~ at high temperatures, preferably around
the flux point of the coating.
On account of the limited solubility of boric
acid in water, even a saturated solution would add
excessive water to the sodium silicate. Granules.
thermore, the water solubility of my coatings is
materially .reduced as compared to ordinary ' unless very porous, when coated with dilute so
T5 silicate coatings.
dium silicate will usually show poor color devel
Granules coated in accordance with the pres
ent invention may be used as a surfacing for
asphalt shingles and for other decorative or
ornamental purposes.
In the following discussion the term “sodium
silicate" usually designates an aqueous solution
of speci?c gravity 1.40 to 1.43 of the neutral sili
cate of commerce which is composed of NazO and
SiO: in the‘ molar ratio of approximately 1 to 3.25,v
25 and contains about 38 to 39 per cent of. solids,
i. e.,non-volatile.
One theory which has been advanced to ex
plain the e?iorescing tendency of the usual
sodium silicate granule coatings is that the SiOz
If dry, powdered boric acid in the amount of _
0.5 to 1.0 grams be added to ten grams of sodium
silicate, precipitation occurs immediately. Owing
to this well known phenomenon, these substances
are generally considered as incompatible. -If
stirred, the mixture becomes full of gritty lumps
and may even assume 'a solid form.
Such mix
tures cannot be uniformly distributed over'the
‘surfaces of refractory granules.
I have found, however, that by causing this re
action to take place on the surfaces of refractory
granules, and subsequently heating the granules,
uniformly coated granules will be produced which
30' portion of the coating is so weakly acidic that it
have excellent qualities as far as bloom and
allows sodium hydroxide to form by hydrolysis
which then combines with the carbon dioxide of
the atmosphere. According to another theory,
weather resistance, water insolubility and adhe
siveness‘to asphalt shingles or the like are con
cerned, particularly ‘where coloring material is
incorporated in the coating.
The colored coatings on such granulesundergo
certain color changes during the heating process.
They lose water and the boric acid undoubtedly
passes through the stages of metaboric acid,
tetraboric acid, etc. I consider 600° F. approxi
mately the lower heating limit ‘required for
Weather resistance in such coatings when applied
carbon dioxide (or carbonic acid) is more strongly
acidic than silicon dioxide (or silicic acid),.and
in the presence of moisture the carbon dioxide dis
places the silicon dioxide from combination with
the sodium oxide or hydroxide.
Without accepting or rejecting these theories,
~10 I ?nd that the presence of carbon dioxide in ef—
?ores'cence can usually be demonstrated quite
easily by treating it with a drop of hydrochloric
The absorption of atmospheric carbon dioxide
45 by sodium silicate could be prevented by the addi
tion of the proper amounts of acids stronger than
carbonic acid.
to most granular bases.
The colors are clean
and bright. As the temperature of the heat treat
ment is raised the color progressively lightens, and
will be lighest at 1200-1250n F. The color will
darken as the temperature is increased to 1300
However, uponthe addition of
1350° F. and even up to 1500° F. in some cases.
even the weakest acids to sodium silicate, either
precipitation or gelling usually occurs. This ap
plies also to boric acid. If boric acid in dilute
solution is added to sodium silicate at ‘room tem
At higher temperatures, up to 1800-1900° F. the
color will again lighten. Of course, the above
perature, there is no apparent immediate action,
though gelling may occur later, but the quantity
of water required to introduce an appreciable
55 amount of boric acid in this way so dilutes the
mentioned temperatures are the maximum at—
tained during the heat treatment, and these color
variations are observed only after the cooling of
the granules.
The melting point of boric acid is about 365° F.
The starting material, orthoboric acid, loses water 55
of constitution at 212° F. and changes'progres"
sively at higher temperatures, ultimately yield
ing boric oxide. Orthoborlc acid, as well as the
intermediate heat products up to and including
boric oxide, are all quite soluble in hot water.
Granule coatings comprising only boric oxide or
boric acid, unless heated to fairly high tempera
tures, have little or no weather resistance andv
are easily dissolved in hot water.
Sodium silicate coated granules are also soluble
in hot water in inverse ratio, roughly, to the tem
perature of their heat'treatment.
Refractory granules coated with sodium sili
cate and boric acid together not only bloom less
15 and much more slowly, but are much less soluble
upon protracted extraction in hot water than
like granules coated with sodium silicate.
In practicing my process, I proceed to mix the
ingredients in one of a number of different ways,
20 ‘three of which I_ shall now describe on a labo
ratory scale,_using small quantities of materials,
a small container and a wooden stick for stir
ring. In all three methods I shall use the same
formula, consisting of granular mineral mate-'
25 rial such as
_ 100
the latter occur, bare or uncolored surfaces will
appear in the granules after the heat treatment,
reducing their attractiveness, or at least the uni
formity‘ of their color effect, and .this is usually
undesirable. Although I have speci?ed one-half
minute in the examples, I do not wish to limit
my process in its application to that exact time,
since I find that the length of time is also re
lated to the vigorousness and efficiency of ‘the
mixing equipment.
In production, I find that from 30 seconds to '
45 seconds mixing in a Stedman mixer (2 ton
capacity) charged with one ton of granules,
driven at 71/2 revolutions per minute produces
the desired coating. The 30 to 45 seconds of 15
mixing refer only to the stage where the sodium
‘silicate and the powdered boric acid are being
mixed on the granules, and not to the total _mix
ing time, which may vary considerably depend
ing upon the method employed and the order in 20
which the various ingredients are added. Al
though I have shown three methods for mixing,
it will be evident to one versed in the art that
other variations are possible; consequently I do
not wish to limit myself to any mixing method
or mixing devices or any maximum or minimum
amount of time employed therein, for I consider
' Chrome oxide ____ _'_ __________________ __ _
that my, invention covers broadly all processes
Dry, powdered boric\acid.. _________ ____'__
of manipulation substantially equivalent to the
treatment described.
30 Sodium silicate____-_ _________________ __
It will also be evident that one mixing method
Mixing methods
may be better adapted than others to granules
(A) Pour the granular slate into ‘the container
and add the boric acid. Stir thoroughly for, say,
35 two minutes. Then add the chrome oxide and
stir for about 1/2 minute. Then add the sodium
silicate and stir vigorously for about 1/2 minute.
Proceed to heating treatment.
(3) Pour the granular slate, the chrome oxide’
of a certain nature, and that the method best
adapted to one kind of granules need not neces
sarily be best adapted to all kinds of granules,
and, further, that two or more of the methods
given may produce approximately equal results
on one kind of granules.- On account of varia
tions in any one type of stone (or type of brick,
or slag or speci?c minerals, etc.) depending
and the sodium silicate together. into the con
tainer and stir; for from 1/2 minute to 3 minutes upon geographic occurrence, method of crush
or longer (or, alternatively, mix the chrome ox ' ing, etc., it is quite impossible here to lay down
hard and fast rules for the particular mixing
ides and the sodium silicate into a roughly dis
persed paint, add this to the slate granules and method or‘modi?cation thereof best adapted to
stir for from‘ 1/2 minute to 3 minutes or longer). each kind of refractory granular base, but from 45
my experience I know that at least one of the
Then add the powdered boric acid and stir vigor
ouslyfor 1/2 minute. Proceed to heating treat
(C) First stir together for about 1 minute the
50 sodium silicate and the chrome oxide in the mix-'
ing container (or in a separate container) to
produce a roughly dispersed paint. Then com
bine this paint, the slate granules, add the pow
dered boric acid in the mixing container, and
55 stir vigorously for 1/2 minute. Proceed to heat
ing treatment.
In practice, method C occurs usually as a
' combination of methods A and B wherein some
of the individual granules are first coated with
sodium silicate and subsequently coated with
boric acid and other individual granules are ?rst
coated with boric acid and then with sodium
In the examples illustrating the type of mix
65, ing procedure I use, several variations and modi
?cations are shown, but in all three methods the
length of time the sodium silicate and powdered
boric acid are ‘mixed together on the granules
is one-half minute. This is an important feature
of my process, because too short‘ a mixing time
results in incomplete distribution of the boric
acid in the sodium silicate, whereas too long or
.. too much mixing results in scraping the wet oo
agulatedlcolored coating o?! some of the surfaces
of certain percentage of the granules. Should
methods will produce well coatedgranules by
my process on any refractory granular base.
Other methods of combining sodium silicate
and boric acid may also be practicable. A solu 50
tion of boric acid may, for instance, be appliedv
to the base and then dried before the application
of the sodium silicate. In such casesthe boric
acid should be dry or nearly dry when the so
dium silicate is applied.
My process could be applied to hot slag or
other heated granules by ?rst diluting the so
dium silicate with su?icient water to allow the
granules to be quenched and cooled thereby,
while still maintaining ‘some of the sodium sili
cate on the surface moist, and then rapidly mix
ing on the boric-acid. Other methods will occur
to those skilled in the art. Coloring matter may
be added along with the sodium silicate or later,
Heat treatment
Pour the ‘wet mixed granules mixed in accord
ance with methods A, B, or C into a metal dish
(or tray) or the like. Preferably the tray should
be hot. Transfer to a furnace,‘ and stir occa
sionally with-a long metal handled, wide, single
toothed’ rake to prevent caking of the granules
during the early stages of the heating. The fun
nace is preferably heated to a temperature slight- 75
lyvhigher than desired before introducing the tray
of granules, so that the granules will quickly come
to the desired temperature, and thus ' the total
heating period need not exceed ten minutes. Usu
ally only ?ve to seven minutes are required. At
the end of the heating period, remove the tray of
granules ‘from the furnace and allow the gran
of at least 600° F. is necessary in my' process to
produce colored coated granules with good weath
ering properties, there are certain blast furnace
slags which may produce colored coated granu
lar material with good weathering properties in
my process at temperatures below 600° F. during
ules to cool, either in the tray in air, or by cooling
the heat treatment, and I ?nd that such granules
possess less tendency to e?loresce than‘if made in
the bottom of the tray in water, or by pouring
accordance with other methods.
10 from the tray to an air-cooled or water-cooled
surface of metal or stone. If desired, water may
be sprinkled on the hot graniiles to assist in cool
ing, but the amount of water thus used should not
be excessive. ' Otherwise the granules will be wet
15 when cooled and will have to be dried afterwards.
The temperatures I employ during the heating
Although in the mixing examples, I have de
scribed slate as the granular base material, I do
not wish to restrict the application of my process
to slate.
I ?nd it is adaptable to many other
granular bases of a refractory character, whether
of mineral or ceramic origin.
For some of the
applications of my coated granules, I ?nd other
treatment depend upon the color desired in the ' bases are even better suited than slate. For ex
?nal product. 'If the slate granules mixed as in ample, I may use this coating in coloring dust
A, B or C be heated for ?ve minutes'at-a tem
>free sand to be used in children’s play boxes, for,
20 perature between 600° F. and 1200° F., the color when colored, it provides an attractive material
of the cooled granules will be of a pleasing yel
of greater insolubility in water than ordinary sili
lowish-‘green or bluish-green shade. Tempera
cate coated granules, and is free from any dan
tures below 1000° F. tend to produce the yellow
gerous or harmful ingredients, such as uncom-v
ish-green colors, being more intense at the lower bined lead compounds, etc., which may occur in
some types of glass-coated granules. The gran 25
25 temperatures and gradually changing to the blu
ish~green at' the higher temperatures. Thus, by ules are quite free from dust.
controlling the temperature, (all other factors be
Other granular refractory bases which I have
ing equal) the color maybe maintained quite uni
employed include feldspar, sandstone, limestone,
form, or various colors may be produced from the
'30 same formula simply by establishing different
temperatures for the heat treatment.
If the temperature employed during the heat
treatment exceeds about 1250“ F., further changes
in color occur,‘ tending to darkenthe shade of
35 green, of the product as the temperature is raised.
In my heating equipment, wherein the pyrometer
tip is located about one inch above the surface
of the granules in the tray, this darkening of
‘ shade appears noticeable about 1280° F. and be
comes more pronounced at higher temperatures,
such as 1400° F. or 1500" F. Above this tempera
ture, the hot granules assume a sticky condition
traprock, shale, quartzite, brick, broken glass,
greenstone, granite, slag, quartz, basalt and dia 30
base, and I ?nd that practically anyrefractory
rock can be color-coated by my process, although
all bases are not suitable for producing the same
color. The choice of base provides further varia
tions in color effects from the same formula, and 35
unless the granular base tends too greatly to dis
integrate or in other ways to change during the
mixing or heat treatment or afterwards, nearly
any base, within reason, may be used to produce
colored granular material of commercial value by 40,
my process.
Some slates are too greatly changed by heating
noticeable if raked, and melting of the coating
above 1500° F. to have colorv appeal, but’ even,
occurs. When a granular base such as sand is
these I ?nd can be greatly improved in color,
45 used, this molten coating assumes a condition of
sticky fluidity or sloughing, and if the temperature using the same total amount of coloring principle
is further raised above 1600°_1750° F., the vfluidity by a double coating and double heating operation.
may gradually diminish and the heated granules The heat treatment employed on the ?rst coating
may show a tendency to become crusty. Upon need not be above 1100° F. to provide greater re
50 cooling, such granules may be light in color and jsistances in the second coat to heating in the
1500“ F. and above temperature range. Certain
more desirable for some uses than either the gran
ules prepared by heating in the ranges 600° to ‘ “greenstone," granite, limestone and traprock
1200° F. or 1200° to 1600° F.
bases likewise are not suited for heating above In heat treating on a manufacturing scale gran
1000° F. when attempting to produce some colors
55 ules coated and colored as above described, I may
use an inclined rotary kiln for a continuous proc
ess, or other types of heating devices if “batch
heating” is preferred. I do not wish to limit my
process to any particular heating ‘device. I prefer,
60 however, that the heat treating devices be so
designed and operated as to provide either expo
sure of the granules to heat in thin layers or agi
- tition or rotation to insure uniform heating.
because of color changes in the base material or
for other reasons,‘ but the colors produced by
heating to temperatures at which the rock is
stable, may be very desirable.
In the preceding examples, I have used pow
dered boric acid and sodium silicate in the pro 60
portions of 5 lbs. of the former and 100 lbs. of the
latter per ton of granules. I have found that the
proportion of materials may not vary greatly in
hesion between the coated granules while wet is
not an obstacle that must be overcome mechan
my process, if the desired results are to be ob
tained. I This is especially true if the subsequent
ically, since granular material coated in accord
heating treatment of the coated granules is con
ance with my invention as distinguished from
ducted below the ?uxing point of the coating. To - '
“silicate granules” has less tendency. to ball up
or form lumps during the early stages of the
produce boric acid-sodium silicate coated gran
ules which are substantially free from the tend
heating process.
ency to form a ‘carbonate bloom, three or four "T:
I do not wish to limit my process to speci?c tem
The temperatures employed should
not be suf?ciently high completely to fuse the
granular base material.- Although on “most min‘.
.75 eral material of natural origin, a temperature
percent of boric acid on the weight of the sodium
silicate per ton of granules is necessary. Smaller
amounts exert a correspondingly smaller effect.
More than ten percent of boric acid appears to
‘alter the relationship necessary between boric 76
perature at which they have been previously heat
acid and sodium silicate for good weather resist
ing colored granules, and I have not found ' treated, and the fact that granules prepared by
higher boric acid percentages of any particular my process show decreased total extractible solu
value in my process, regardless of the tempera
ture employed. However, since the amount of
ble salts, indicate that my process produces a
coating imwhich the sodium (or NaaO) is more
sodium silicate used per ton of granules may be ?rmly held than in silicate coatings. This is
varied, depending upon the kind of granular base ' borne out also by the greater resistance to bloom
used, the shape, porosity, and size of the indi
vidual granules and whether one or two or more
of my coatings.
Disregarding solution of, or chemical reaction
coats be applied thereto, etc., I prefer to express
with coloring agents, my process results in “so 10
boric acid used, based on the weight of sodium
other coloring matter will give a satisfactory
sodium-boro-silicate coating only if heated to a 15
the relationship, not in terms of pounds or per- _ dium-boro-silicate” coatings on the granules;
hence, I refer to ‘the product as “boro-silicate
'centages of boric acid per ton of granular ma
terial, but in terms of the percentage of powdered granules.” Borax, silica and chrome oxide or
15 silicate employed. This relationship, calculating
boricLacid as 56.4% non-volatile, and sodium
silicate as being approximately 40% non-volatile,
and comprising one part NaaO to 325 parts of
Si 02 is as follows:
relatively high temperature, above approximately
1300° F. My coating having the above desired
qualities can be produced at any temperature
above 600° F., or with certain bases, even lower.
This results in great fuel economy and a much 20
wider choice of granular base. Also coating ma-,
Percent by weight
terials consisting of silica, chrome oxide, boric
Si 0:
Minimum ________________________ _.
4. 23
Maximum _______________ ___ _______ __
14. 10
1 acid or boric oxide and sodium hydroxide or so
_ 76
dium carbonate would produce a sodium-boro
silicate coating only if heated to 1300 F. or 25
What I claim is:
1. The process'of coating granules of refrac
The minimum percent of B203 (4.23) is equiva
tory material comprising the following .steps:
lent to 3 lbs. of powdered boric acid‘per 100 lbs. mixing together sodium silicate and chrome oxide 30
30 of sodium silicate, and the maximum (14.10) is
to produce a roughly dispersed paint, mixing to
equivalent to 10 lbs. of powdered boric acid per gether the paint, the granules and powdered boric
100 lbs. of sodium silicate. For practical pur
acid, and heating the coated granules.
poses I ?nd that from four to six percent of boric
acid on the weight of the sodium silicate is both
85 economical and effective, yetit will‘be evident
2. The process of coating granules of refrac-
tory material comprising the ‘following steps:
mixing the granules, sodium silicate and color
that slight departures from my maximum and ing matter together uniformly to-coat the gran- '
minimum amounts maybe used without depart— . ules, then applying to the wet coating on the
ing from the spirit of my invention.
surfaces of the granules dry, powdered boric acid,
Although I have illustrated with a sodium and ?nally heating the granules.
40 silicate solution of approximately 40% solids, in
3. The process of coating granules of refractory
which sodium oxide and silicon dioxideare pres
material comprising‘ the following steps, mixing
“ ent in the ratio of approximately 1:3.25, it will
the granules and sodium silicate together uni
be evident that solutions‘of other solids content, formly to coat the granules, mixing with the
such as 35% solids or less up to 512% solids or
coated granules dry, powdered boric acid, and 45
slightly more, wherein the solids may consist of
sodium oxide and silicon dioxide in ratios rang
ing from 1:3.0 up to 1:4.0, may be used without
departing from the spirit of my invention.
In the examples I have used chrome oxide as
the color principle. I do not wish to restrict my
self to the use of any specific color principle, nor
to any particular amount of color principle, since
a wide range and variety of color imparting ma
terials may be used alone or in combinations, in
‘ eluding ultramarines, metal oxides and other
compounds, themselves stable colors or capable
of being converted into colored oxides or stable
forms of colored materials under the coating
and/or heating treatment, etc.
The decreased solubility of coatings on gran
ules produced by my process as compared to sili
cate coatings prepared under the same condi
tions (same base, same mixing time, same heat
ing operation, etc.) indicates that the coating
produced by my process is not merely a silicate
coating. Boric acid is a water soluble substance,
and I find that extraction in distilled water for
twelve hours at 175° F.’ or higher, will dissolve
a relatively large quantity of it. Silicate gran
.70 ules likewise show a distinct solubility during
twelve hours extraction, depending upon the tem
heating the granules.
4. The process of coating granules of refraca
tory material comprising the following steps: uni
formly coating the granules with sodium silicate
and pigment, mixing the coated granules with
dry, powdered boric acid, and heating the gran
5. The process of coating. granules of refrac
tory material comprising the following steps:
coating the granules with pigmented sodium sili
cate, mixing the coated granules with dry, pow~
dered boric acid, and heating the granules.
6. The process de?ned in claim 5 and in which
the relationship between the ingredients is as fol
lows, expressed in per cent by weight: B20; 60
4.234410%, NazO 24%, S10: 76% or approxi
mately 3-10 lbs. of powdered boric acid per 100
lbs. of sodium silicate.
'7. The process de?ned in claim 5 and in which
the weight of the powdered boric acid is less than
10% of the weight of the sodium silicate.
8. The process de?ned in claim 5 and in which
the weight of the powdered boric acid is 3-4%
of the weight of the sodium silicate.
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